Improved Production of Neospora caninum Oocysts, Cyclical Oral Transmission between Dogs and Cattle, and In vitro Isolation from Oocysts

Abstract

Scarce information is available about Neospora caninum oocysts and sporozoites, in part because only small numbers of oocysts have typically been produced by experimentally infected dogs. We hypothesized that I reason for low experimental production of oocysts is that dogs have been fed tissues from experimentally infected mice instead of tissues from cattle (which are natural intermediate hosts of N. caninum). In this study, 9 dogs were fed tissues from N. caninum-infected calves, and oocyst production was compared with 6 dogs that were fed infected mouse carcasses. The number of oocysts produced by dogs that ingested infected calf tissues (mean = 160,700) was significantly greater (P = 0.03) than the number of oocysts shed by dogs that ingested infected mice (mean = 5,400). The second goal of our experiment was to demonstrate cyclical oral transmission of N. caninum between dogs and cattle. As few as 300 oocysts were used to successfully infect calves, and tissues from these calves induced patent infections in 2 of 3 dogs; oocysts from I of these dogs were administered to another calf, and tissues from this calf subsequently induced a third dog to shed oocysts. Oocysts were confirmed to be N. caninum using a species-specific polymerase chain reaction technique. In addition, sporulated oocysts were used to recover N. caninum in vitro after digestion in an acid-pepsin solution and inoculation of cell monolayers.

Coyotes (Canis latrans) are definitive hosts of Neospora caninum

“…The minimum infectious dose of N. caninum oocysts needed to infect cattle is not known, but it is no more than 300 oocysts (Gondim et al, 2002). In the present study using coyotes, one 12-week-old pup shed approximately 500 oocysts.…”

“…1A). The unsporulated oocysts were spherical to subspherical and measured 10 mm in diameter ðn ¼ 10Þ: They were aerated in 2% H 2 SO 4 as previously described (Gondim et al, 2002). After aeration, sporulated oocysts contained two sporocysts, each with sporozoites (Fig.…”

“…Faecal samples were collected for 4 days before the coyotes were infected with calf tissues, and for 28 days after infection. Faeces were examined by a standard sucrose flotation technique as described earlier (Gondim et al, 2002). No N. caninum-like oocysts were observed in any specimens prior to consuming the infected tissues, although Isospora spp.…”

“…The three calves were infected during the first week of life with N. caninum. Calf 1 was injected intravenously with 5 £ 10 5 tachyzoites (NC-Illinois strain; Gondim et al, 2002), calf 2 was injected intravenously with a mixture of 1 £ 10 6 tachyzoites of NC-beef strain (McAllister et al, 1998(McAllister et al, , 2000 and NC-Illinois strain (5 £ 10 5 tachyzoites from each strain), and calf 3 was orally administered 29,000 oocysts of the NC-beef strain via an oesophageal feeder. Calves were euthanised 6-12 weeks after infection.…”

Intrauterine Neospora caninum inoculation of heifers and cows using contaminated semen with different numbers of tachyzoites

“…Epidemiological evidence also suggests horizontal transmission [6,8]. Calves [9] and pregnant cows [10] can be experimentally infected by oral administration of Neospora oocyst shed by dogs, and the N. caninum life cycle has been reproduced by cyclical oral transmission between dogs and cattle [11]. In addition, a sylvatic transmission cycle of N. caninum between cervids (white-tailed deer) and canids (dogs, coyotes) has been demonstrated in North America [12].…”